1. Field of Invention
The present invention relates to an electronic circuit, electronic device, method of driving the electronic circuit, electro-optical device, and electronic equipment.
2. Description of Related Art
In the related art, electro-optical devices employing an organic EL element can be used as a display. The electro-optical device employing the organic EL element uses an active-matrix addressing method as one of various driving methods.
In the active-matrix addressed electro-optical device, pixel circuit is arranged for each organic EL element to control luminance of the EL element. The luminance gradation of the organic EL element is controlled by supplying a holding capacitor of the pixel circuit with a data signal (in voltage value or current value) responsive to the luminance gradation. Namely, the holding capacitor is charged with an electric charge responsive to a set luminance gradation.
The conduction state of a driving TFT (Thin-Film Transistor) is set in response to an amount of electric charge held in the holding capacitor, and a current in accordance with the conduction state is fed to the organic EL element, as disclosed in PCT Publication WO98/36406.
The pixel circuit includes at least one active element, such as a transistor, and it is difficult to cause all active-elements to have strictly uniform characteristics. In particular, a thin-film transistor (TFT) forming a pixel circuit of a display is subject to large variations in characteristics. For this reason, it is difficult to achieve a desired luminance in response to a predetermined input signal.
Characteristics of the display also vary with the aging of an active element forming the pixel circuit or electro-optical device.
The present invention addresses or overcomes the above and/or other problems, and provides an electronic circuit, electronic device, method of driving the electronic circuit, electro-optical device, and electronic equipment to detect operational characteristics of the electronic circuit at a high precision.
A first electronic device of the present invention includes a plurality of unit circuits. Each of the unit circuits includes a first transistor, a holding element to hold an electrical signal, supplied through the first transistor, as an amount of electricity, a second transistor, the conduction state of which is controlled in accordance with the amount of electricity held by the holding element, a driven element which is supplied with an amount of current in response to the conduction state, and a third transistor which is connected in series with the second transistor. The electronic device is connected through the third transistor to a tester which detects the amount of current.
By turning on the third transistor, the amount of current responsive to the amount of electric charge from the second transistor to be supplied to the driven element is obtained through the third transistor. The operational characteristics of the electronic circuit are thus detected. The third transistor may be arranged in each of the unit circuits, or may be shared by several of the plurality of unit circuits.
A second electronic device of the present invention includes a plurality of unit circuits. Each of the unit circuits includes a first transistor, a holding element to hold an electrical signal, supplied through the first transistor, as an amount of electricity, a second transistor, the conduction state of which is controlled in accordance with the amount of electricity held by the holding element, and a driven element which is supplied with an amount of current responsive to the conduction state. The second transistor is connected in series with the first transistor, and wherein the electronic device is connected through the first transistor to a tester which detects the amount of current.
An exemplary embodiment corresponding to the second electronic device is a fourth exemplary embodiment discussed subsequently. The electronic device has a circuit arrangement supplied with a current signal as the electrical signal.
In the electronic device, a fourth transistor is connected between the driven element and the second transistor.
With this arrangement, one of the third transistor and the first transistor is turned on with the fourth transistor turned off to cut off the supply of a current to the driven element, and thus the amount of current flowing through the second transistor to be supplied to the driven element can be detected using the one of the third transistor and the first transistor. During the current detection period of the tester, at least the fourth transistor preferably remains in an off state.
In the above electronic device, the driven element may be a current driven element, such as an organic EL element. A light emission layer of the organic EL element is fabricated of an organic material.
In the electronic device, the third transistor is preferably arranged in each of the unit circuits. With this arrangement, the current characteristics of each of the plurality of unit circuits are detected.
In the electronic device, the holding element may be a capacitive element that holds, as an electric charge, an electrical signal supplied to each of the plurality of unit circuits.
In the electronic device, the holding element may be a memory element, such as an SRAM.
The electronic device includes a memory circuit which stores a correction value to an electrical signal fed through the first transistor and determined by the tester.
With this arrangement, the correction value stored in the memory circuit is used to correct the operational characteristics of the electronic device, and the operation of the driven element is thus adjusted.
A driving method of the present invention of driving an electronic device including a first transistor, a holding element to hold an electrical signal, supplied through the first transistor, as an amount of electricity, a second transistor, the conduction state of which is controlled in accordance with the amount of electricity held by the holding element, a driven element which is supplied with an amount of current responsive to the conduction state, and a third transistor connected in series with the second transistor, includes: holding the amount of electricity on the holding element based on the electrical signal by turning on the first transistor, and detecting the amount of current flowing through a current passage containing the second transistor and the third transistor with the third transistor turned on to electrically connect the second transistor through the third transistor to a tester to detect the amount of current.
With this arrangement, the tester can detect the amount of current to be supplied to the driven element.
In the driving method of driving the electronic device, preferably, the current passage excludes the driven element.
In the driving method of driving the electronic device, the driven element may be a current driven element, such as an organic EL element.
A first electro-optical device of the present invention includes a plurality of pixel circuits, each pixel circuit arranged at an intersection of each of a plurality of scanning lines and each of a plurality of data lines, and the pixel circuit includes a first transistor, the conduction of which is controlled by a scanning signal supplied through a corresponding scanning line of the plurality of scanning lines, a holding element which holds, as an amount of electricity, a data signal supplied through a corresponding data line of the plurality of data lines and the first transistor, a second transistor, the conduction state of which is controlled by the amount of electricity held by the holding element, an electro-optical element supplied with an amount of current responsive to the conduction state, and a third transistor connected in series with the second transistor. Each of the plurality of pixel circuits is connected through the third transistor to a tester which detects the amount of current.
In the electro-optical device, the third transistor may be arranged in each of the unit circuits, or may be shared by several of the plurality of unit circuits.
In the electro-optical device, the third transistor may be connected to the tester through data lines corresponding to the plurality of transistors. With this arrangement, the data line can be used as a test line without arranging a dedicated test line.
A second electro-optical device of the present invention includes a plurality of pixel circuits, each pixel circuit being arranged at an intersection of each of a plurality of scanning lines and each of a plurality of data lines. Each pixel circuit includes a first transistor, the conduction of which is controlled by a scanning signal supplied through a corresponding scanning line of the plurality of scanning lines, a holding element which holds, as an amount of electricity, a data signal supplied through a corresponding data line of the plurality of data lines and the first transistor, a second transistor, the conduction state of which is controlled by the amount of electricity held by the holding element, the second transistor connected in series with the first transistor, and an electro-optical element supplied with an amount of current responsive to the conduction state. Each of the plurality of pixel circuits is connected through the first transistor to a tester which detects the amount of current.
In the electro-optical device, the tester includes a current detecting circuit to detect the amount of current, a correction value calculating circuit to determine a correction value to the electrical signal based on the amount of current detected by the current detecting circuit, and a memory circuit to store the correction value to the pixel circuit. In setting the electrical signal, the electrical signal is corrected by the correction value.
In this arrangement, the correction value calculating circuit determines a correction value to adjust variations in the operational characteristics of the pixel circuit, and the memory circuit stores the correction value to the pixel circuit. The operational characteristics of the pixel circuit are corrected in accordance with the correction value to the electronic circuit stored in the memory circuit, and the operation of the driven element can be thus adjusted.
Electronic equipment of the present invention incorporates one of the above-described electro-optical devices.